Mdwarfs

Mdwarfs, or M-type dwarfs, are a class of small, cool stars on the main sequence. They are the most common type of star in the Milky Way, composing a large fraction of the galactic stellar population.

Physically, Mdwarfs have low masses and low luminosities. Their masses range from about 0.08 to 0.6 solar masses and radii from roughly 0.1 to 0.6 solar radii. Surface temperatures lie between about 2,400 and 3,700 kelvin, giving them a red appearance and very low luminosities, typically a thousandth to a few percent of the Sun’s. Stars at the lower end of the mass range are fully convective, which has implications for their magnetic activity and dynamos.

Mdwarfs burn hydrogen slowly on the main sequence and have extremely long lifetimes—trillions of years for the lowest-mass examples. Because of this longevity, many Mdwarfs will persist for a very long time; their evolution proceeds toward white dwarfs only after leaving the main sequence in the distant future.

The habitable zone around an Mdwarf lies close to the star. This makes planets in the HZ easier to detect by transits and radial velocity, but also raises questions about tidal locking and exposure to stellar flares, which can affect atmospheres and potential habitability. A large number of exoplanets have been found around Mdwarfs, including several in or near the HZ.

Observationally, Mdwarfs are fundamental targets for planet surveys, transit missions, and microlensing studies. Their small size boosts the relative transit depth for Earth-size planets, aiding discovery, while their activity cycles can complicate measurements.